CancelAsync Method

Summary

Cancels a pending asynchronous operation.

Syntax

C++

Java

public void CancelAsync()

Public Sub CancelAsync()

public void cancelAsync(Object operation)

public: 
void CancelAsync();

Remarks

NOTE: This topic is part of RasterCodecs Async support using the .NET System.ComponentMode.AsyncOperation model. For .NET async/await support this type/member is not used. Instead, refer to RasterCodecs Async Operations.

The RasterCodecs object supports getting information, loading and saving image files asynchronously through the use of the GetInformationAsync, LoadAsync, LoadSvgAsync and SaveAsync methods. These methods will use an internal WebClient object to perform their operations and this object will be created automatically on the first call to these methods and can be accessed through the AsyncWebClient property.

If it is desired to create the WebClient object manually (for example, to subscribe to any of its event or set the credentials prior to invoking any read operations), you can call UseAsync to create the object, change its behavior and then call GetInformationAsync, LoadAsync, LoadSvgAsync or SaveAsync.

Note: UseAsync, AsyncWebClient, IsAsyncBusy, and CancelAsync are only applicable when the GetInformationAsync, LoadAsync, LoadSvgAsync or SaveAsync was with the versions that take a Uri parameter. The versions that take a String or a Stream do not use a WebClient object internally.

If you want to check the progress or cancel the operation, then use the LoadImage event as normal.

Example

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void CancelAsyncExample() 
{ 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
   Uri uri = new Uri(srcFileName); 
 
   RasterCodecs codecs = new RasterCodecs(); 
 
   // Now Load the file asynchronously 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(cancelAsyncExample_LoadAsyncCompleted); 
   RasterImage image = codecs.LoadAsync(uri, null); 
 
   // Cancel it immediatly, in normal situation, the cancelation will happen 
   // before the LoadAsync method has a chance to load the file and 
   // the message "User canceled" will be displayed on the console 
   if (codecs.IsAsyncBusy) 
   { 
      codecs.CancelAsync(); 
   } 
} 
 
private void cancelAsyncExample_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e) 
{ 
   if (e.Cancelled) 
   { 
      Console.WriteLine("User canceled"); 
   } 
   else if (e.Error != null) 
   { 
      Console.WriteLine("Error: " + e.Error.Message); 
   } 
   else 
   { 
      // Get the image 
      RasterImage image = e.Image; 
      Console.WriteLine("Image loaded asynchronously: Size = {0} by {1}", image.Width, image.Height); 
      image.Dispose(); 
   } 
 
   // Unsubscribe to the event and dispose the RasterCodecs object 
   RasterCodecs codecs = sender as RasterCodecs; 
   codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(cancelAsyncExample_LoadAsyncCompleted); 
   codecs.Dispose(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; 
}

Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.ImageProcessing 
Imports Leadtools.ImageProcessing.Color 
Imports Leadtools.Drawing 
Imports Leadtools.Svg 
 
Public Sub CancelAsyncExample() 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp") 
   Dim uri As New Uri(srcFileName) 
 
   Dim codecs As New RasterCodecs() 
 
   ' Now Load the file asynchronously 
   AddHandler codecs.LoadAsyncCompleted, AddressOf cancelAsyncExample_LoadAsyncCompleted 
   Dim image As RasterImage = codecs.LoadAsync(uri, Nothing) 
 
   ' Cancel it immediatly, in normal situation, the cancelation will happen 
   ' before the LoadAsync method has a chance to load the file and 
   ' the message "User canceled" will be displayed on the console 
   If codecs.IsAsyncBusy Then 
      codecs.CancelAsync() 
   End If 
End Sub 
 
Private Sub cancelAsyncExample_LoadAsyncCompleted(ByVal sender As Object, ByVal e As CodecsLoadAsyncCompletedEventArgs) 
   If e.Cancelled Then 
      Console.WriteLine("User canceled") 
   ElseIf Not IsNothing(e.Error) Then 
      Console.WriteLine("Error: " + e.Error.Message) 
   Else 
      ' Get the image 
      Dim image As RasterImage = e.Image 
      Console.WriteLine("Image loaded asynchronously: Size = {0} by {1}", image.Width, image.Height) 
      image.Dispose() 
   End If 
 
   ' Unsubscribe to the event and dispose the RasterCodecs object 
   Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs) 
   RemoveHandler codecs.LoadAsyncCompleted, AddressOf cancelAsyncExample_LoadAsyncCompleted 
   codecs.Dispose() 
End Sub 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class

Requirements

Target Platforms

Reference

RasterCodecs Class

RasterCodecs Members

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Help Version 20.0.2020.4.3